Most of the manual here addresses Message mode, and C-c C-c directly
above cites the Message mode command, not the Mail mode command.
* doc/emacs/sending.texi (Mail Sending): Fix reference. (Bug#39639)
@findex message-send
@vindex message-kill-buffer-on-exit
The usual command to send a message is @kbd{C-c C-c}
-(@code{mail-send-and-exit}). This sends the message and then
+(@code{message-send-and-exit}). This sends the message and then
buries the mail buffer, putting it at the lowest priority for
reselection. If you want it to kill the mail buffer instead, change
the variable @code{message-kill-buffer-on-exit} to @code{t}.